Ground waters are becoming increasingly contaminated by halogenated chemicals, herbicides, pesticides, and various other toxic organic compounds. Sources of contamination include pollution from industrial effluents and accidental chemical spills, leakage of leachates from landfills, and agricultural application of chemicals to crops and soils. Many of these organic compounds are volatile (VOCs) and are capable of removal by air-stripping or vacuum-stripping from groundwaters. More troublesome, on the other hand, are semivolatile organic compounds (SVOCs) and some virtually nonvolatile organic compounds such as polychlorinated biphenyls (PCBs), halogenated pesticides, phosphonate esters such as some herbicides, and the like. These organic compounds are generally sparingly soluble in ground waters. Their concentration levels are often in the part-per-billion range or less. Yet, even such extremely low concentrations represent a potential health hazard because of their bioaccumulative nature. Such low concentrations may be amenable to detection and analysis under carefully controlled laboratory conditions with state-of-the-art instrumentation. Not so readily accomplished, however, is onsite field sampling with simultaneous detection and analysis of such low concentrations.
For example, the U.S. Environmental Protection Agency recommends gas chromatographic analyses for detection of pesticides by established methods (EPA-608{4}, 8151{5}, and 8141A{6}). The method detection limits (MDL) for these analytical techniques are in the range of 0.01 to 1.0 ppb. These methods require large sample volumes and elaborate procedures for collection, preservation, handling and cleaning. To maintain consistency, the expensive gas chromatographs must be calibrated in accord with formal quality control programs. Such methods are inefficient for on-line monitoring of groundwater pollutants. Nor are they appropriate for detection and semi-quantitative monitoring of groundwater contamination. A need remains for efficient preconcentration and sampling techniques combined with sensitive instruments more suited to field sampling sites.
U.S. Pat. No. 4,960,520 discloses a method of removing evaporable contaminants from aqueous solutions by transfer through a gas phase membrane into a stripping solvent. This method involves the use of a microporous membrane having a gas retained in its micropores (hence, the term "gas phase membrane"), with the contaminated aqueous fluid passing in contact with a first face of the membrane and a nonaqueous strippant passing in contact with a second face. A coating of a polymerized disiloxane is deposited on the second face to prohibit penetration of the strippant into the micropores, so as not to displace the entrained gas. This method, being limited to evapotable contaminants, is useful for concentrating volatile organic compounds into a strippant fluid. It has little or no utility for stripping semivolatile compounds because of their low vapor pressure, and appears not to be applicable to virtually (i.e., practically or essentially) nonvolatile compounds such as pesticides and polycyclic aromatic hydrocarbons (PAHs) having Henry's constants of less than about 0.0005 at STP (standard temperature and pressure).
It is an object of this invention to provide a method for concentration of semivolatile and essentially nonvolatile organic compounds from aqueous solutions into an organic solvent.
It is another object of this invention to provide a method by which up to a 10,000-fold concentration of semivolatile or essentially nonvolatile organic compounds may be achieved in an organic solvent in ratio to their aqueous concentrations, starting with highly dilute solutions of the compounds in aqueous solutions such as a contaminated groundwater.
It is an additional object of this invention to provide a method by which onsite field sampling with simultaneous detection and analysis of such low concentrations of semivolatile and essentially nonvolatile organic compounds may be accomplished.
Additional objects, advantages and novel features of the invention will be set forth in the description of the invention which follows, and in part will become apparent to those skilled in the art upon review of the following or as may be learned through practice of the invention.